Intrinsic Signal Imaging of Macaque Fundus to Reveal Two-dimensional Functional Map of the Retina

Abstract

Abstract: : Purpose: Optical imaging with intrinsic signals visualizes metabolic changes elicited by neural activation and, recently, has been applied to ocular fundus to detect the visually evoked response in cat and human retina (Grinvald et al. 2002, ARVO). This technique provides two-dimensional functional structure of the retina, which is essential for the clinical application of this technique to detect the local disorders in human ocular fundus. In order to evaluate the correspondence between the lesion site and the optical signal decrease, we have coagulated part of Macaque retina by laser photocoagulation, by which retinal pigment epithelial (RPE) and photoreceptor cells were locally damaged, and measured the optical signals at various sites. Methods: Ocular fundus of Macaque monkey, illuminated by various wavelength of lights (480nm, 540nm, 610nm, 700nm and 900nm), was monitored by a fundus camera system equipped with a near infrared CCD camera. The intrinsic signal evoked by full field white flash stimulus (duration: 1.0 msec) was calculated by dividing the averaged images obtained after stimulus by those obtained during a 1-second period before the stimulus onset. Retinal function map was constructed by overlaying the signal intensity map on fundus photograph. Results: In normal ocular fundus, flash stimulus evoked global absorption increase, peaking 3 to 5 seconds after stimulus onset, within the posterior vascular arcades. Optical signal intensity varied depending both on the recording sites and on the wavelength of illumination. In the eye photocoagulation was given, the peak amplitude of the optical signal in normal sites was 1.5 to 3.0 times larger than in the corresponding photocoagulation site. The two-dimensional signal map clearly distinguished a low signal intensity area, whose edge precisely corresponded with the border of photocoagulation. Conclusions: Intrinsic signal imaging could clearly distinguish the functionally damaged area in Macaque ocular fundus, although at present we can not distinguish the lesion in photoreceptor and RPE cells from that in the microcirculation of retina. This technique may be available for monitoring the neuronal activity of retina non-invasively, in the eyes with retinal vascular disorders, retinal degenerative diseases, glaucoma, etc.

Keywords: retina • imaging/image analysis: clinical